Hey Erin,
I haven't had this happen to me, but I've never taken any of those drugs either. Like Mary and Rach said, it could be caused by your kidneys or liver so see your GP as soon as you can so you can get the labs done. Did your neuro think it could be caused by the cellcept since that's when it started? Take care and hope you get some answers soon.
Hugs,
Pat